Do you have the Break In switch on the front panel set to "ON"? It's the switch just below the AGC speed selector
If so, check terminal 9 for 6.3 vac. (or maybe 12.6 vac, I forget which). If you don't hear a relay click, when grounding terminal 9 AND the break in switch is ON, then either the relay is bad, or the ac voltage to the relay (through the BRK IN terminal) is interrupted somewhere. If you can hear the relay close, and the radio still doesn't mute, then something else is amiss.
Grant
On Dec 1, 2009, at 9:49 PM, John King wrote:
> Thanks for the reply, Grant. My R 390 doesn't mute when terminal 9 is grounded. I have connected an alligator clip lead to terminal 9 and then connected the other end of the clip lead to terminal 16 which is ground and there is no effect. I can't figure out why there is no effect when terminal 9 is grounded. What do you think, Grant? I do not have a manual or schematic for the R390. 73, John, K5PGW